The goal of this project is to assess the efficacy of a new treatment for hypophonia (decreased vocal loudness) associated with Parkinson's disease (PD). Current speech therapy strategies for hypophonia focus on increasing sound pressure level. It is clear from previous research that that increasing loudness affects respiratory, laryngeal, and articulatory function in healthy adults and that training individuals with PD to increase loudness can impact multiple dimensions of speech production. Based on preliminary studies from our laboratory, we propose a treatment plan which will use a voice- activated appliance which delivers monaural multi-talker babble noise while the individual speaks, stimulating louder speech (the Lombard Effect). The Lombard Effect reflects the fact that speakers will naturally and automatically speak louder under conditions of background noise. The proposed treatment plan differs from existing treatment plans in that it takes place during everyday speaking contexts, outside of what could be considered traditional delivery paradigms. The benefits of the treatment plan are that individuals with PD will wear the appliance in natural communication contexts, potentially achieving a louder, clearer, and more intelligible voice, without needing to self-cue. The first specific aim of this project is to assess improvements in vocal intensity, speech intelligibility and clarity, and communicative competence as the result of an 8-week treatment plan. Because individuals with dysarthria can make changes in the respiratory, laryngeal, and articulatory speech subsystems to improve overall speech output, it is important to examine each subsystem simultaneously. The second specific aim of the project is to identify the underlying speech mechanisms for therapy-related improvements using physiologic measurements of respiratory strength, respiratory kinematics during speech, laryngeal aerodynamics, and articulatory acoustics. The third specific aim is to determine the long-term maintenance of speech treatment gains, across a six-month period, in one group of patients continuing treatment and in one group for whom treatment is withdrawn. Because the treatment is designed to train the individuals, the fourth specific aim is to examine the immediate generalization of treatment effects to a noncued context. Lastly, because variability is reflective of neuromotor control status, the fifth specific aim is to document underlying neuromotor control in individuals with PD pre- and post-treatment. Parkinson's disease (PD) affects a significant number of individuals in the U.S. population. Treatment of speech disorders associated with PD is difficult due to the multiple factors which are likely to affect the speech of individuals with PD and the way those factors may limit the generalization and maintenance of treatment gains. The intervention proposed is unique because it provides a naturalistic external cue and trains the individuals during activities of daily living.